1. Technical Field
The disclosure relates to an optical sensor which can detect light level and light level rate and direction of change.
2. General Description of the Problem
Kitchen and bathroom cabinets, particularly those below countertops, are often dark even with the cabinet door open and the room where the cabinet is located has a high level of ambient lighting. Adding light sources within cabinets is often difficult because these areas do not typically have outlet plugs. To simplify the installation of lighting, battery operated lights have been used. The use of lighting in these areas is typically brief and intermittent and to conserve battery power the lights are designed to switch states, such as from on to off or off to on, with opening and closing of the cabinet door, and sometimes after a short period after opening of the door. This has been accomplished by any one of a number of devices including mechanical switches, magnetic switches, ultrasonic motion sensors, microwave motion sensors, active and passive infrared motion sensors and photoelectric sensors combined with timers.
Mechanical and magnetic switches can be attached directly to the cabinet door and/or door frame and if properly installed reliably detect whether or not the door is open or closed. The light operated by the switch turns on immediately when the door is opened and turns off immediately upon its closure. A timer can also be built in to turn the light off after a predetermined period of time if the door is left open. In order to make sure the contacts are closed when the cabinet door is closed, these types of switches must be mounted to the door and/or door frame in such a manner that they align properly when the door is closed. Achieving proper alignment of contacts during installation can make installation difficult where poor installation might keep the product from operating properly. In cases where two doors are used, as is often the case under sinks, two sets of switches are installed, which increases the chance of installation error. These types of switches use wires that run from the switch on the door frame to the lighting device which is usually installed off the door inside the cabinet. The wires are vulnerable to damage as items are placed in or removed from the cabinet.
Using motion sensors to control interior cabinet light activation can simplify installation by reducing the number of components to install and eliminating exposed wires inside the cabinet. A variety of motion sensor technologies exist including, ultrasonic, microwave and passive infrared motion sensors that can reliably generate signals in response to cabinet door movement. They tend to be less reliable in distinguishing the direction of movement. They also distinguish poorly between opened and closed stationary doors. As a result they can fail to turn a light off immediately upon closure of the door and in some instances can turn the light on when the door is being closed. Passive infrared motion sensors may not work if an object is placed in the cabinet at a location which obstructs the field of view of the light collecting lens. Passive infrared motion sensors tend to exhibit a noticeable delay from initial movement of the door until the light turns on. Microwave motion sensors generate microwaves which can penetrate the door and turn on the light when there is motion adjacent to the cabinet even if the door is not moved.
Active infrared motion sensors respond to motion and are used for lighting control. These devices typically use a light emitting diode (LED) to emit infrared light in front of the sensor. An infrared photodiode or transistor detects the infrared light upon reflection by nearby objects. Changes in the detected amount of infrared light indicate motion in front of the sensor. One such device is the General Electric LED Motion Sensing Light Model #17433. This device detects motion within a few inches in front of the sensor. When used in a cabinet the system does not respond immediately when the door is opened but responds upon someone reaching into the cabinet. As with passive infrared motion sensors, this type of sensor is sensitive to field of view considerations.
Photoelectric sensors can also be used to turn on a light when a door is opened. This type of sensor detects the increase in light level when a door is opened and turns on a light.
An example of a photoelectric sensor product is the Automatic Closet Light; model EZT-ACL, from Touch and Glow Lighting Solutions. This alternating current (AC) product is screwed into an ordinary light bulb socket and then a light bulb may be screwed into it. The light bulb turns on when the door is opened for a period of time that is user selectable. The product uses a single, fixed light level threshold to determine if the door is open or closed. Under conditions of low ambient room lighting the light level in the closet may never rise above the threshold when the door is opened. In a bright environment the light level may not drop below the threshold when the door is closed and again the light will not turn on when the door is opened. The product does not differentiate between slowly changing light levels, as when a door opens, and fast changes in light level as when a room light is turned on.
Ambient light sensors are also used in vehicles and with hand held electronic devices to control the illumination levels of displays, typically increasing brightness of the display as ambient light levels increase. U.S. Pat. No. 7,297,929 teaches a multi-element sensor for detecting light over wide angles and in multiple optical zones. Detected light level values are stored and luminosity of a light source determined based on historic (i.e. the stored) light readings.